The development of so called direct reflex measurements (electro optic distance measurement without cooperative targets or prisms) has enabled accurate measuring of remote point without locating a physical target, such as a prism, and hence enabled possibilities for one person distance measuring.
There are two main electro optic distance measurement technologies, namely time of flight and phase shift.
The time of flight method is based on the use of short pulses sent from a measurement apparatus, reflected off a target, and detected back at the measurement apparatus. The distance to the target is calculated by means of round trip measurements for the pulses.
The phase shift method uses phase shift measurement of reflexes off a target of a beam sent from the measurement apparatus instead of roundtrip measurements.
In prior art time of flight methods, a limited measuring time interval is normally chosen in order to limit the processing time for identification of desired reflex pulses and in order to avoid identification of reflex pulses from objects in the same line of sight as the desired target. This is normally done by setting a measuring time interval corresponding to a range of distances within which the target is estimated to be, i.e. if the target is estimated to be within a distance range, the measuring apparatus is set to look for reflex pulses within a time interval corresponding to the roundtrip time for light for that distance range.